Parallel detector fire alarm system



Jan. 6, 1959 v T. w. BLAND ETAL PARALLEL DETECTOR FIRE ALARM SYSTEM Filed Jan. 14. 1955 2 Sheets-Sheet 1 Jan. 6, 1959 T. w. BLAND ET AL PARALLEL DETECTOR ETRE ALARM SYSTEM 2 Sheets--Sheeil 2 Filed Jan. 14. 1955 Hanson-.F

INVENTORS TMO/w45 w @LA/vo ,e LESTER A- OBE/EN BY Unite This invention relates to lire alarm systems of the supervised type, and more particularly to an improved re alarm system of the aforesaid type having a parallel detector circuit.

A main object of the invention is to provide a novel and improved fire alarm system of the parallel detector circuit type, said system being provided. with means for operating an alarm device upon a predetermined rise in temperature in the detector circuit thereof, and being also provided with means for giving an alarm when the detector circuit is interrupted.

A further object of the invention is to provide an improved re alarm system of the type having a parallel detector circuit including normally open thermally responsive elements arranged to shunt the detector circuit upon a predetermined rise in temperature, the system including a supervisory device for giving an alarm signal when the detector circuit or associated circuitry in series with the detector circuit is broken or interrupted, the system being further provided with means for substituting an auxiliary power source when the main power source thereof fails, so that the system will be operable under all circumstances.

A still further object of the invention is to provide an improved fire alarm system of the supervised type having a parallel detector circuit, said system being provided with indicating means showing the availability of the main source of power for the system and being provided with means for substituting an auxiliary power source upon failure of the main source of power, the system being further provided with means for testing the alarm devices thereof and with means for manually silencing the alarm devices thereof, indicating means being provided to give notice that the alarm devices have been silenced.

A still further object of the invention is to provide an improved lire alarm system of the parallel detector type which includes means for supervising the integrity of the system, the system including a plurality of detector circuits which may be physically spaced by considerable distances, the various detector circuits being arranged to operate respective alarm relays, the energization of any one of said relays providing actuation of alarm means at a central station.

A still further object of the invention is to provide an improved fire alarm system of the parallel detector type, said system including a normally energized supervisory relay and a normally deenergized alarm relay, the interruption of the common circuit of the alarm relay and the supervisory relay causing the operation of a trouble signal, the detector circuit being arranged so that it is normally of relatively high resistance and undergoes a substantial reduction in resistance under conditions of abnormally high temperature, the change in resistance of the detector circuit causing an inverse change in the circuit including the alarm relay, whereby said alarm relay becomes energized and operates a fire alarm signal.

A still further object of the invention is to provide an` atent 2 cally spaced detector circuits, the circuits being powered by a conventional power supply of the alternating current type and being provided with means for boosting the voltage of the power supply to compensate for losses in the lines connecting the power supply to the remote stations, the system being further provided with means for. substituting a battery-derived power source for the normal power supply upon the failure of said normal power supply, means being provided for inverting the battery voltage to transform the battery voltage to the same type of alternating current power as that of the normal power supply.

Further objects and advantages of the invention will be'- come apparent from the following description and claims, and from the accompanying drawings, wherein:

Figure la is an electrical wiring diagram illustrating one portion of an improved fire alarm system constructed in accordance with the present invention, showing the means for substituting the auxiliary power supply upon failure of the main power supply and showing a pair of detector circuits, one of said detector circuits being connected to a remote station.

Figure lb is a wiring diagram illustrating the remaining portion of the re alarm system, showing the interconnections of the stations associated with the detector circuits illustrated in Figure la.

Referring to the drawings, and more particularly to Figure la, Ztl and 21 designate respective line wires connected to a conventional alternating current power supply source, such as a ll7 volt alternating current power line commonly employed in household systems. The line wires 20 and 21 are connected to the respective terminals of the primary 22 of a step-down transformer 23 having the secondary 24 which is connected by respective wires 25 and 26 to the winding 28 of a relay 27, said relay having the armature 29 which is normally raised, as shown in Figure la, when the relay winding 28 is energized, and which descends from the position of Figure 1a when the winding 28 becomes deenergized. Armature 29 is provided with the upper contact 30 which normally engages the stationary contact 31 when the armature 29 is in its elevated position shown in Figure 1a. Designated at 32 and 33 are respective lower contacts which are engageable by respective contacts 34 and 35 carried by the armature 29 when the relay winding 2S is deenergized.

Designated at 436 is a step-down transformer having the primary winding 37 and the secondary winding 38. The terminals of the primary winding 37 are respectively connected to terminals a and b. The' terminal b is connectedl to the line wire 20 by a wire 39. The terminal a is connected by respective wires ,40 and 41 to the contact 31. The contact 30 is connected by a wire 42 to the line wire 21. Thus, with the relay 27 energized, namely, with the normal power supply available, the primary 37 of transformer 36 is connected to the line wires 20 and Z1 through the relay contacts 30 and 31.

Designated at 42 is a storage battery having one terminal thereof connected to-a wire 43 which is connected 'to one terminal of the secondary 24 of the step-down transformer 23. The other terminal of the step-down transformer secondary 24 is connected by a wire 44 through a condenser 45 and a rectier 46 to the remaining terminal of battery 42, shown at 47. This defines a charging circuit for the battery 42 wherein alternating current from the secondary 24 of the step-down transformer 23 lis rectified by the rectifier 46 and is employed to charge the battery 42 while the normal power supply at the line wires 20 and 21 is available. The condenser 45 is employed to block the return passage of direct curren-t from the battery 42 to the transformer secondary 24 when the line wires 20 and 21 are disconnected from the power source, or when said power source fails.

Patented Jan. 6, 1959 Designated' at 48 is aconventional inverter of` the viv brator type having the vibratory armature 49 connected to the wire 43 and having the electromagnet 50 and the usual step-up transformer 51. The primary 52 of the transformer 51 has itsA terminals connected to respective stationary vibrator contacts 53 and 54. As shown, the

electromagnet 50 is connected by a wire 55 to the contact 54 and by another wire 56 to the wire 43. The cen-l ter tap of the primary Winding 52 is connected by a wire 57 to the armature contact 34'. VThe stationary relay contact 32 is connected by a wire 58 to the battery terminal 47.

Designated at 59 and 60 are respective stationary vibrator contacts engageable by the armature 49 as a result of the vibration of said armature, the contact 69 being connected by a wire 61 to one terminal of the secondary 62 of transformer 51` and the contact 59 being connected by a wire' 73 to the opposite terminal of transformer secondary The second set of contacts 60 and 59 are provided in the inverter should it be desired to rectify the alternating current appearing at the terminals of the secondary winding 62. However, in the typical embodiment of the system presently to be described, the second set of contacts 60 and 59 need not be employed.

As shown, the wire 61 is connected to a wire 63, which in turn is connected to the terminal b. The wire 73 is connected to a wire 64, which in turn is connected t to the relay contact 33. A pilot lamp 65 is connected across wires 64 and 63.

It will be understood that the inverter 48 is normally deenergized, because the contacts 32 and 34 are normally separated. However, should the main source of power fail, the armature 29 is released, causing the contacts 32 and 34 to close, whereby the inverter is energized by the battery 42, as by a circuit comprising battery 42, wire 47, wire 58, contact 32, contact 34, Wire 57, theV lower half of the transformer primary winding 2, a wire 66, wire 55, electromagnet winding 50, wire 56, and wire 43. When the armature 49 is moved downwardly, electromagnet winding 50 is short circuited by the engagement of the armature 49 with the contacts 54, causing the armature 49 to be released and causing said armature to engage the upper contact 53 wherein the upper half of the winding 52 is connected to the battery 42. Thisy procedure continues at the natural frequency of vibration of the armature 49, in the well known manner, causing periodic pulsations of current in the transformer primary 52 which produce alternating current at the terminals of the secondary winding 62. This produces alternating current voltage across the power terminals a and b, since one terminal of secondary winding 62 is connected by the wire 61 to the wire 63 and the other terminal of the secondary 62 is connected by the wire 73 to the wire 64, which is connected through contacts 33 and 35 and wire 40 to power terminal a. A condenser 67 is connected across the terminals of the secondary 62 of transformer 51 to eliminate radio interference.

The transformer 51 is designed to produce substantially the same output voltage at the terminals a and b as normally appears across the power line wires 20 and 21. Thus, when the main power supply fails, the same operating voltage is available at the terminals a and b as is normally provided by the line wires 20 and 21. The failure of the normal power sourceand the resultant substitution of the inverter power source is indicated by the energization of the pilot lamp 65, which occurs when contacts 33 and 35 close.

Designated a-t 68'is a terminal strip having the respective terminals 1 to 12, as shown in Figure la. terminal of the secondary of transformer 36 is connected through a fuse 69 and a wire 70 to the terminal 5. The other terminal of transformer secondary 38 is connected by a wire 7l to the' terminal 6. Designated at 72V is' a trouble alarm bell whose terminals are connected by wires 74 and 75 to the respective terminals 3 and 4. Designated at 76 is a lirst re alarm bell whose terminals are connected by respective wires 77 and 78 to the terminals 7 and 8. Designated at 79 is a second lire alarm bell whose terminals are connected by respective wires 80 and 81 to the terminals 9 and 10. Designated at 82 is a battery employed for operating the trouble alarm bells, the terminals of the battery being connected by respective wires 83 and 84 to the terminals 1 and 2.

Designated generally at 85 is a first detector circuit which is terminated by an adjustable resistance 86, the detector circuit comprising the respective wires 87 and 88 connected to the respective terminals 11 and 12. Connected in parallel across the wires 87 and 88 are the respective thermally responsive, normally open detector elements 89, said detector elements being spaced along the detector circuit line wires 87 and 88 and being arranged to close upon a predetermined rise in temperature, whereby to shunt the terminating resistance 86 and to substantially reduce the resistance of the detector circuit.

Designated generally at 94) is a second detector circuit, which is generally similarto the detector circuit 85 but which may be remotely located therefrom, as in a remotely located area o-f the region being protected by the system. The detector circuit 99 includes the adjustable terminating resistance 91 and the spaced detector units 89 which are connected between the detector circuit line wires 92 and 93. Wire 92 is connected to a terminal 13 of an auxiliary terminal strip 94. The line wire 93 is connected through the secondary 95 of a booster transformer 96 to the terminal 14 on the terminal strip 94. The primary of the booster transformer 96 is connected to the power supply terminals a and b, as shown in Figure la, in any suitable manner, so as to boost the voltage applied to thedetector circuit 96 to compensate for'losses which may be present due to excessive lengths of the conductors employed therein, namely, the line wires 92 and 93.

The primary winding of the booster transformer 96 may be connected to the power terminals a and b, or alternatively may be fed from another suitable power supply circuit which may be provided with means for substituting a stand-by source of power in the event of failure of the normal power supply, such as the inverteroperated circuit illustrated in Figure la.

The terminal strip 94 has respective terminals 15 and 16 which may be connected to any suitable annunciator device or other alarm unit which is arranged to be energized by the closure of a circuit between the terminals 15 andl 16, as willV be presently described.

Referring now to Figure lb, it will be seen that the terminal strip 68 is illustrated having the terminals ll` to 12 thereon, as described in connection with Figure la. Similarly, the terminal strip 94 is illustrated having the terminals 13 to 16' thereon, as described in connection with Figure la. As has been previously described, the signal bell operating battery 82 is connected across the terminals 1 and 2, the trouble signal bell 72 is connected across the terminals 3 and 4, the low voltage power from the secondary of the step-down transformer 36 is connected to the terminals 5 and 6, the fire alarm signal bell 76 is connected to the terminals '7 and 8, the secondv re alarm signal bell 79 is connected to the terminals 9 and lil, and the detector circuit iis connected to the terminals 11 and 12. The detector circuit 99 of the second section of the system is connected to the terminals 13 and 14, and the auxiliary outside lalarm circuit is connected to the terminals 15 `and 1.6 of the terminal strip 94. As shown, the terminals .2 .and 3 are connected together and the terminals 6, 8, 9 'and 11 are connected together. The terminal 7 is connected to the terminal 10, whereby the signal bells 76 and 79 are connected in parallel and are operated simultaneously.

Designated at 97 is a normally deenergized lire alarm relay, and designated at 98 is a normally energized supervisory relay located in a main or central station. Also located in the main or central station are the respective pilot lamps 99, 100 and 101, as well as the stand-by power unit described in connectionl with Figure la and its associated pilot lamp 65. Also located in this station are a manually operated, normally closed reset switch 102, a manually operated test switch 103, a manually operated single pole double throw silencing switch 104 for silencing the tire alarm bells 76 and 79, and a manually operated single pole double throw silencing switch 105 for silencing the trouble alarm bell`72.

There also may be located at the central station a reset switch 106 of the manually operated type and which is normally closed, as shown, employed in conjunction with an alarm relay device 107 associated with the second section of the system, namely the section connected to the detector circuit 90, as will be presently described. Also provided at the central station is the manually operated, normally open test switch 108 and the normally energized supervisory relay 109. The alarm relay 107 is normally deenergized, as will be presently explained.

The winding of the alarm relay 97, shown at 110, is connected in series with the power supply terminals 5 and 6 and the detector circuit terminals 11 and 12 by the following circuit: Power terminal 5, a wire 112, reset switch 102, a wire 113, the winding 110 of relay 97, a wire 114, an adjustable resistance 115, a wire 116, terminal 12, detector circuit 85, terminal 11 and a wire 117 connecting terminal 11 to the remaining power terminal 6. The current flowing in this circuit is normally insufficient to energize the relay 97 unless one of the detector elements 89 closes, as will occur when the predetermined rise in temperature occurs along the detector circuit. As shown, the relay 97 has the armature 113 which is elevated when the relay becomes energized and which is normally in its lowered position, shown in Figure lb. The armature 118 has the upper contacts 119 and 120 engageable respectively with stationary contacts 121 and 122, and has the lower contact 123 engageable with a stationary contact 124.

The supervisory relay 98 is normally energized by a circuit as follows: Terminal 5, wire 112, a current limiting resistor 125, a wire 126, the winding 111 of relay 98, a wire 127, contacts 124 and 123, a wire 129, wire 114, resistor 115, wire 116, terminal 12, detector circuit 85, terminal 11, and wire 117 to the remaining power terminal 6. Thus, relay 98 is energized as long as the foregoing circuit remains intact. The relay 98 is provided with the armature 130 having the upper contact 131 engageable with a stationary contact 132, and the lower contact 133 engageable with a stationary contact 134. Normally, when the relay is energized, the upper contact 131 engages the stationary contact 132.

A resistor 135 is connected across the contacts 124 and 123 of relay 97 to maintain the original planned voltage on the coil of supervisory relay 98, when alarm relay 97 becomes energized and opens contacts 123 and 124. (Note that when detector 89, Figure la, shunts out resistor 86, the voltage in the coil of supervisory relay 98 would increase to a dangerous value if auxiliary resistance were not inserted into the circuit to replace resistor 86. Therefore resistor 135 is automatically inserted into the circuit by opening contacts 124 and 123 and causing current to then flow through resistor 135, which is normally shunted out of the circuit by normally closed contacts 123 and 124.)

When the supervised circuit opens, namely, the detector circuit 85, for any reason, the relay 98 becomes deenergized, allowing contact 133 to engage contact 134, thereby completing an energizing circuit for the trouble signal bell 72, as follows: Terminal 4 of the trouble alarm bell 72,

a wire 136, contact 134, contact 133, a wire 137, stationi ary contact` 138 of the silencing switch 105, pole 139 of switch 105, a wire 140, terminal 1, battery 82, terminal 2, and a wire 141 connecting terminal 2 to the signal bell terminal 3. This circuit energizes the trouble signal bell 72 from the battery 82, and the trouble signal may be silenced by moving the pole 139 from the position thereof shown in Figure 1b into engagement with the opposite stationary contact 142 of the switch 105. This silences the bell but energizes the trouble alarm pilot lamp 101 by a circuit comprising battery terminal 1, wire 140, pole 139, switch contact 142, a wire 143, pilot lamp 101, and a wire 144 from the pilot lamp to the terminal 2 connected to battery 82.

When one of the thermally responsive elements 89 closes, due to an abnormal rise in temperature, the terminating resistance 86 becomes shunted, substantially reducing the resistance o f the detector circuit 85, and causing the alarm relay 97 to become energized. This elevates the armature 118 of the relay 97 and energizes the alarm bells 76 and 79, as well as establishes a holding circuit for the relay 97. The holding circuit is established as follows: Power terminal 5, wire 112, reset switch 102, wire 113, winding 110 of the relay 97, wire 114, contact 122, contact 120, a wire 145, a wire 146, and Wire 156 connected to contact 6 leading to the power supply. Relay 97 will thus be maintained energized until reset switch 102 is opened. The closing of contacts 119 and 121 energizes the re alarm signal bells 76 and 79 by the following circuit: Signal terminals 7 and 10, a wire 147, contacts 131 and 132, a wire 148, contact 119, contact 121, a wire 149, stationary contact 150 of silencing switch 104, pole 151 of switch 104, a wire 152, wire 112, power terminal 5, the power supply, power terminal 6, and the wire 117 connecting power terminal 6 to the terminals 8 and 9 of the signal bells. The signal bells can be silenced by moving the pole 151 into contact with the opposite stationary contact 153 of switch 104. This energizes the pilot lamp by a circuit comprising power terminal 5, wire 112, wire 152, pole 151, contact 153, a wire 154, pilot lamp 100, a wire 155, wire 146, and a wire 156 connecting wire 146 to the power terminal 6.

The signal relay 97 can be reset by depressing the push button switch 102, opening said switch and releasing the holding circuit for the relay winding 110, allowing the armature 118 to drop to its normal position, assuming that the detector circuit 85 has been likewise returned to a normal condition wherein its thermally responsive elements 89 are opened.

The relay 97 may be energized for testing purpose by means of the test switch 103 which is connected so that when said switch is closed the winding is energized by the following circuit: Power terminal 6, wire 156, wire 146, test switch 103, a wire 157, wire 114, winding 110, wire 113, reset switch 102, wire 112, and power terminal 5.

The resistor is made adjustable so that the current in the detector circuit may be adjusted in accordance with variations in utility voltage connected to the primary 22 of the transformer 23.

The supervisory relay 109 of the second section has the winding 160 which is normally energized from the secondary 161 of a step-down transformer 162 by the following circuit: Secondary 161, a wire 163, normally closed reset switch 106, a wire 164, winding 160, a wire 165, normally closed contacts 123 and 124 of the normally deenergized signal relay 107, a wire 166, a wire 167, the winding 168 of signal relay 107, a wire 169 connected to terminal 14, detector circuit 90, terminals 13, a wire 170, and a wire 171 connected between wire and the remaining terminal of the secondary 161. The primary winding 172 of the transformer 162 is connected to the respective power terminals a and b. A resistor 173 is connected across the contacts 123 and 124 to maintain the original planned voltage on the coil of supervisory relay 109. Should the supervisory relay 109 at the central station will become energized by the following circuit: Trouble signal contact 4, wire 136, a wire 174, a stationary lower contact 175 of relay 1079', contact 176, the wire 137", the wire 137, the stationary contact 138 of the silencing switch 105, pole 139, Wire 140, battery terminal 1, the battery 82, battery terminal 2, wire 141, and signal contact 3.

When any one of the thermally responsive elements 89 in the detector circuit 89 closes, as by an abnormal rise in temperature, the terminating resistance 91 of the detector circuit 90 is shunted, substantially reducing the resistance of the detector circuit, and increasing the current in the series circuit including the relay windings 168 and 160, and the secondary 161 of transformer 162. The rise in current is sufficient toenergize the relay 107, which in turn energizes the alarm relay 97 at the central station by the following circuit: Power terminal 6, wire 156, an upper stationary contact 121 of relay 107, the armature contact 119', a wire 177, the upper stationary contact 132 of the supervisory relay 109, the armature contact 131 of said supervisory relay, a wire 178, wire 114, winding 110 of the relay 97, wire 113, reset switch 102, wire 112, and power terminal 5. Energization of the main signal relay 97 causes the alarm signal bells 76 and 79 to become energized by the circuits above described. The holding circuit for the relay 97 is also established and said relay will remain energized until the reset switch 102 is opened. The remote relay 107 will remain energized by the closure of a holding circuit therefor comprising transformer secondary 161, wire 171, wire 170, a wire 180, a stationary upper contact 181, an armature contact 182, a wire 183, the wire 169, relay Winding 168, wire 167, a resistor 173, winding 160 of the supervisory relay 109', wire 164, reset switch 106; and wire 163 connected to the remaining terminal of the transformer secondary 161. Thus, the alarm relay 107 will remain energized until the reset switch 106 is opened.

The energization of the remote signal relay 107 causes closure of an armature contact 134 of said relay with a stationary contact 185 thereof, said contacts being connected to the respective terminals and 16, whereby the outside alarm device will be energized by the closure of said contacts 184 and 185, resulting from the energization of the alarm relay 107.

The test switch 10S is connected between the wires 170 and 169, whereby the relay 168 may be energized manually by closing said test switch (producing the same effect as the closure of the contacts 131 and 182), whereby the operation of the second portion of the system may be testedin substantially the same manner as that of the first portion of the system, previously described, in connection with the test switch 103. In the event of a break in the detector circuit 90, both relays 107 and 109 become deenergized, whereby the normally energized relay 109 closes its contacts 175 and 176 and opens its contacts 131 and 132. The closure of the'contacts 175 and 176 causes the trouble signal bell 72 to become energized as above described. The opening of the con'- tacts 131 and 132 prevents a false alarm from being given by the alarm signal relay 107 since the above described circuit for energizing the main alarm signal relay 97 is opened at the contacts 131 and 132.

When the co-ntacts 123 and 124 of the alarm signal relay 97 open, the resistor 135 is inserted in the circuit including the winding 111 of the supervisory relay 98, the resistor 135 having a suitable value to maintain substantially normal current through the winding 111,

namely the same current as flows through said winding when the terminating resistance 86 of the detector circuit 85 is not shunted by the closure of one of the thermally responsive elements S9. Similarly, when the contacts 123 and 124 of the remote signal relay 107 open, the resistor 173 is inserted in the circuit including the winding 160 of supervisory relay 109, maintaining the proper 8 current conditions in the supervisory relay Winding to maintain said winding energized, namely the conditions existing prior to the shunting of the terminating resistance 91 of the detector circuit 90 by the closure of one of the thermally responsive elements 89 in the detector circuit 90. The insertion of the resistor 173'limits the current in the relay winding to a safe value when the terminating resistance 91 is shunted and thereby prevents damage to said relay winding.

While a specific embodiment of an improved fire alarm system of the supervisory type has been disclosed in the foregoing description, it will be understood that' various modifications within the spirit of the invention may occur to those skilled in the art. Therefore, it is intended that no limitations be placed on the invention except as defined by the scope of the appended claims.

What is claimed is:

1. In a fire alarm system of the type having a detector circuit comprising a resistance and a normally open thermally responsive element arranged to shunt saidV resistance upon a predetermined rise in temperature, a normally deenergized firealarm relay device and a normally energized supervisory relay device connected in parallel with each other, a first source of current, circuit means connecting said source in series with said ydetector circuit and the parallel-connected relay devices', al second source of current, means arranged to connected said second` source to the seriescircuit in place of the firstnamed source in response to failure of said first source, the normal current in the series circuit being insufficient to energize saidy fire alarm relay device but beingy suiiicient to maintain said supervisory relay device energized, the fire alarm relay device being energized when said thermally responsive element closes, first signal means operated in response to energization of said re alarm relay device, and second signal means operated in response to deenergization of said supervisory relay device.

2. In la fire alarm system of the type having a detector circuit comprising a resistance and a normally open thermally responsive element arranged to shunt said resistance upon a predetermined rise in temperature, a4 normally deenergized fire alarm relay device and a normally energized supervisory relay device connected in parallel with each other, a first source of current, circuit-means connecting said source in series with said detector circuit and the parallel-connected relay devices, a second source of current, means arranged to connect said second source to the series circuit in place of thev first-named source in response to failure of said first source, a normally deenergized indicator element, means energizing said indicator element when said second source is connected to the series circuit, the normal current in the series circuit being insufficient to energize said fire alarm relay device but being sufficient to maintain said supervisory: relay device energized, the fire alarm relay' device'beingenergized when said thermally responsive element closes, first signal means operated in response to energization ofsaid fire alarm relay device, and second signal means operated lin response to deenergization of said supervisory relay device.

3. In a fire alarm system of the type having a detector circuit comprising a resistance and a normally open thermally responsive element arranged to shunt said resistance' upon a predetermined rise in temperature, a normally deenergized fire alarm relay device and a normally energized' supervisory relay ydevice connected in parallel with each' other, a first source of current, circuit means connecting saidv source in series with said detectorcircuit andthe parallel-connected relay devices, a second source of current, means arranged to connect said second source to the' series circuit in place of the first-named source in response to failure of said first source, a normally deenergized indicator element, means energizing said indicator. element when said second source is connect to the series circuit, the normal current in the series circuit being insulicient to energize said re alarm relay device but being suicient to maintain said supervisory relay device energized, the lire alarm relay device being energized when said thermally responsive element closes, rst signal means operated in response to energization of said re alarm relay device, a holding circuit arranged to maintain said lire alarm relay device energized after an initial energization thereof, a normally closed manually operable reset switch in said holding circuit, and second signal means operated in response to deenergization of said supervisory relay device.

4. In a tire alarm system of the ytype having a detector circuit comprising a resistance and a normally open thermally responsive element arranged to shunt said resistance upon a predetermined rise in temperature, a normally deenergized lire alarm relay device and a normally energized supervisory relay device connected in parallel with each other, a source of current, circuit means connecting said source in series with said detector circuit and the parallel-connected relay devices, the normal -current in the series circuit being insuicient to energize said re alarm relay device but being suliicient to maintain said supervisory relay device energized, the lire alarm relay device being energized w-hen said thermally responsive element closes, irst -signal means operated in response to energization of said fire alarm relay device, second signal means operated in response to deenergization of said supervisory relay device, a second detector circuit co-mprising a second resistance and a normally open thermally responsive element arranged to shunt -said resistance upon a predetermined rise in temperature, a normally deenergized fire alarm relay device and a normally energized supervisory relay device connected in series with said second detector circuit, a second current source connected to said second detector circuit, the normal current in said second detector circuit being insuicient to energize said second re alarm relay device but being sutlcient to maintain .said second-named supervisory relay device energized,` the second fire alarm relay device being energized when said second-named thermally responsive element closes, and means Afor energizing said first-named lire alarm relay device when said second lire alarm relay device becomes energized.

5. In a fire alarm system of the type having a detector circuit comprising a resistance and a normally open thermally responsive element arranged to shunt said resistance upon a predetermined rise in temperature, a normally deenergized lire alarm relay device and a normally energized supervisory relay device connected in parallel wi-th each other, circuit means connecting ysaid source of current in series, a source of current connected in circuit with said detector circuit and the parallel-connected relay devices, the normal current in the series circuit being insucient to energize said fire alarm relay device but being sufficient to maintain said supervisory relay device energized, the re alarm relay device being energized when V said thermally responsive element closes, rst signal means operated in response to energization of Said fire alarm relay device, second signal means operated in response to deenergization of said supervisory relay device, a second detector circuit comprising a second resistance and a normally open thermally responsive element arranged vto shunt said second resistance upon a predetermined rise in temperature, -a normally deenergized second fire alarm relay device and a normally energized lsupervisory relay device connected in series with said second detector circuit, a .second current source connected to said seco-nd detector circuit, the normal current in said second detector circuit being insuicient to energize said second re alarm relay device but being suflicient to maintain said secondnamed supervisory relay device energized, the second fire alarm Arelay device being energized when said secondnamed thermally responsive element closes, and means for energizing said rst-named lire alarm relay device when lsaid second lire alarm relay device becomes energized, said last-named means comprising a normally open pair of contacts on said second lire alarm relay device connected in series with said first-named source of current and said first-named fire alarm relay device, said l last-named pair of contacts being closed by the energization of said second lire alarm relay device.

6. In a ire alarm lcircuit of the type having a detector circuit comprising a resistance and a normally 1open thermally responsive element arranged to shunt said resistance upon a predetermined rise in temperature, a normally deenergized lire alarm relay device and a normally energized supervisory relay device connected in parallel with each other, a source of altern-ating current, circuit means connecting said source in series with said detector circuit and the parallel-connected relay devices, the normal current in said detector circuit being insuflicient -to energize said fire alarm relay device but being suicient to maintain said supervisory relay device energized, the fire alarm relay device being energized when said thermally responsive element closes, first signal means operated in response to energization of said lire alarm relay device, second Signal means operated in response to deenergiza-tion of said supervisory relay device, an extended alarm circuit and a transformer having its primary winding connected to said source and its secondary winding `connected in series with .said extended alarm circuit.

References Cited in the file of this patent UNITED STATES PATENTS 467,358 Rie@ Jan, 19, 1892 1,927,744 Jones Sept. '19, 1933 2,094,211 Grant Sept. 28, 1937 2,278,939 Muehter Apr. 7, 1942 2,469,001 Poitras May 3, 1949 2,605,342 Spurling July 29, 1952 FOREIGN PATENTSI 274,620 Great Britain July 28, 1927 

